Experiments (1)

Analysis of a diffraction pattern generated by a single crystal. X-rays have a wavelength, typically around 1 Angstrom (the diameter of a hydrogen atom). If a narrow parallel beam of X-rays is directed at a sample of a pure protein, most of the X-rays will pass straight through it. A small fraction, however, will be scattered by the atoms in the sample. If the sample is a well-ordered crystal, the scattered waves will reinforce one another at certain points and will appear as diffraction spots when the X-rays are recorded by a suitable detector. The position and intensity of each spot in the X-ray diffraction pattern contain information about the position and nature of the atoms in the crystal. The three-dimensional structure of a large molecule can be deduced from the electron-density map of its crystal. In recent years X-ray diffraction analysis has become increasingly automated, and now the slowest step is likely to be the production of suitable macromolecule crystals. This requires high concentration of very pure macromolecule and empirical searching for the proper crystallisation conditions.